1. Technical Field
The present invention relates to a lock-up device and particularly to a lock-up device for a fluid coupling for transmitting torque and absorbing and damping torsional vibration.
2. Background Art
There are many cases where a lock-up device for directly transmitting torque from a front cover to a turbine is disposed in torque converters. The lock-up device is equipped with a piston, a drive plate, plural outer peripheral side torsion springs, a driven plate, plural inner peripheral side torsion springs, and a middle member (Japanese Patent Application No. 2001-82577). The piston is coupleable to the front cover. The drive plate is coupled to the piston. The torque is input from the drive plate to the plural outer peripheral side torsion springs. The driven plate is coupled to the turbine. The plural inner peripheral side torsion springs are arranged on the inner peripheral side of the outer peripheral side torsion springs and transmit the torque to the driven plate. The middle member is rotatable relative to the drive plate and the driven plate and transmits the torque from the outer peripheral side torsion springs to the inner peripheral side torsion springs.